The present invention relates to a spherometer for measuring the radius of curvature of a lens by comparing it with that of a reference lens.
A method of measuring the radius of curvature of the rough ground surface of the lens, generally utilizes a ring spherometer.
Such a spherometer is well known, for example, from "Grinding . Polishing" in "Optical Production Technology" 1984 (Japan Optical and Precision Instruments Manufacturer's Association).
FIG. 8 shows an outline of the spherometer. As shown in FIG. 8, a spherometer 101 has a spherical surface measuring section which comprises a dial gauge (display section) 102 and a spherometer ring 104 fitted onto a shaft 103 of the dial gauge 102 and secured by a screw 105. The shaft 103 is provided slidably with a measuring member (rod) 106 which in connected to the dial gauge 102.
The spherometer 101 serves to measure the radius of curvature of the lens by comparing it with the reference lens 107. In this case, the whole periphery of the spherometer ring 104 is placed in contact with the spherical surface and the dial gauge 102 is set at zerovalue. The whole periphery of the spherometer ring 104 is placed in contact with the spherical surface of the lens to be measured 108, thereby measuring the radius of curvature by a numerical value, corresponding to the displacement in the axial direction of the measuring rod 104, which numerical value is shown by the dial gauge 102.
In such radius curvature measuring, due to the spherical surface measuring using a conventional spherometer 101, both the spherometer 101 and the reference lens 107 or the lens to be measured 108 are measured by holding the lenses and spherometer by hands, so that the whole periphery of the spherometer ring 104 of the spherometer 101 may be made in contact with the spherical surfaces of the reference lens 107 and the lens to be measured 108 while adjusting its inclination by hands.
When spherical surface measuring is performed easily and precisely, the spherometer 101, the reference lens 107 and lens to be measured 108 are arranged on a vertically movable device, however, in such an arrangement, the whole periphery of the spherometer ring 104 can not be suitably placed in contact with the spherical surfaces of the reference lens 107 and the lens to be measured 108, so that very small axial shift and an inclination are produced on the axis of the measuring member 106 of the spherometer and precise measuring can not be performed.